Double helix bookcase



FIG. 1 is a perspective view of a double helix bookcase showing my new design;

FIG. 2 is a front elevation thereof;

FIG. 3 is a side elevation thereof;

FIG. 4 is a top plan view thereof; and

FIG. 5 is a bottom plan view thereof.

The design is characterized by the base member as best illustrated in FIGS. 1 and 5. 

The ornamental design for a double helix bookcase, as shown and described. 